WO2024037289A1

WO2024037289A1 - Ultrahigh-concentration shear thickening fluid, preparation method therefor, and use thereof

Info

Publication number: WO2024037289A1
Application number: PCT/CN2023/108862
Authority: WO
Inventors: 张赶年; 石正兵
Original assignee: 中山莱圃新材料有限公司
Priority date: 2022-08-19
Filing date: 2023-07-24
Publication date: 2024-02-22
Also published as: CN115386338A

Abstract

Disclosed are an ultrahigh-concentration shear thickening fluid, a preparation method therefor, and a use thereof. The fluid is composed of nanoparticles and a solvent, the volume fraction of the nanoparticles in the fluid is 0.63-0.65, and the solvent is liquid polyhydric alcohol. The nanoparticles are pre-mixed and then are subjected to strong shear dispersion until a "Tyndall effect" appears, then a high-circulation instrument is used for further mixing uniformly such that the fluid has good uniformity, and finally drying is performed until the total content of small molecule alcohol impurities is not more than 3.5 wt%. The shear thickening fluid of the present invention has a concentration of 0.63-0.65, has a greater thickening amplitude (the ratio of the highest concentration to the lowest concentration is more than 1000 times at most) than that of discontinuous shear thickening of all existing fluids, has a better impact energy absorption effect, and has more significant improvement on the impact resistance of products to which the shear thickening fluid is applied.

Description

An ultra-high concentration shear thickening fluid and its preparation method and application

Technical field

The invention relates to an ultra-high concentration shear thickening fluid and its preparation method and application, and belongs to the technical field of nanofluid materials.

Background technique

Shear thickening fluid is a particle suspension that changes its concentration in response to changes in external forces, and is composed of nanoparticles and solvents. When external force acts on the fluid, the particles gather together to form particle clusters, and the viscosity of the fluid increases exponentially with the formation of particle clusters. When the external force is removed, the particle clusters disband, the particles return to the dispersed and suspended state, and the fluid viscosity also reduces to the equilibrium state. This characteristic enables the fluid to absorb impact, and has potential application markets in many fields such as stab-proof, bullet-proof, and impact-proof.

The ability of a fluid to absorb shock increases dramatically with the increase in the volume fraction φ (concentration) of nanoparticles in the fluid. The highest concentration of fluid reported in the literature is φ=0.62, while the concentrations of other published shear-thickening fluid nanoparticles are basically concentrated in 0.46-0.62. There are currently no reports of ultra-high concentration shear-thickening fluids with φ≥0.63.

The difficulty in preparing ultrahigh-concentration shear-thickening fluids lies in dispersing agglomerated nanoparticles. The existing preparation technologies are mainly vortex oscillation, low-speed ball milling and ultrasonic dispersion. When preparing fluids with medium and low concentrations, these preparation techniques can effectively disperse agglomerated nanoparticles, giving the fluid good shear thickening properties. However, when the fluid concentration rises to 0.63 or higher, the existing technology cannot effectively disperse the agglomerated particles, so the prepared fluid does not have discontinuous shear thickening properties. Therefore, it is necessary to invent a preparation process to effectively disperse agglomerated nanoparticles and prepare shear-thickening fluids with a concentration of 0.63 or higher.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing technology and provide an ultra-high concentration shear thickening fluid with a fluid concentration of 0.63-0.65. The fluid has stable discontinuous shear thickening characteristics and is thickened. The amplitude (the ratio of the highest concentration to the lowest concentration) can exceed 1000 times at most.

Another object of the present invention is to provide a method for preparing the above-mentioned ultra-high concentration shear thickening fluid.

The third object of the present invention is to provide an application of the above-mentioned ultra-high experimental shear thickening fluid.

The purpose of the present invention is achieved through the following technical solutions:

An ultra-high concentration shear thickening fluid is composed of nanoparticles and a solvent, characterized in that the volume fraction of the nanoparticles in the fluid is 0.63-0.65, and the solvent is liquid polyol.

In the present invention, the particle size of the nanoparticles is 250-900 nm, the particle size is monodisperse, and the particle material is an inorganic compound, such as silica or calcium carbonate.

A method for preparing the above-mentioned ultra-high concentration shear thickening fluid, which is characterized by comprising the following steps:

a. Premixing: Slowly add the nanoparticles into the solvent and stir slowly until there are no lumps visible to the naked eye to prepare a premixed liquid;

b. Shear dispersion: The particles in the premixed liquid are strongly sheared and dispersed until the "Tyndall effect" can be observed in the fluid under the irradiation of the laser pointer, and the initial fluid is obtained;

c. Mixing: Use high circulation instruments to further mix the initial fluid to obtain a fluid with good uniformity;

d. Drying: Dry the fluid until the total content of water and small molecule alcohol impurities in the fluid does not exceed 3.5wt% to prepare a discontinuous shear thickening fluid.

In the preparation method of the present invention, the dried fluid can be mixed again by repeating step c to improve the uniformity of the entire fluid. The fluid should be in a uniform state when flowing, without local stratification.

In the present invention, the powerful shearing and dispersing instrument used in shearing and dispersing is a ball mill or bead mill or a three-roller.

In the present invention, the high circulation instrument used for mixing is a vortex oscillator or a bottle roller.

An application of the above-mentioned ultra-high concentration shear thickening fluid can be used for composite stab-proof materials or anti-collision protection bodies.

Compared with the prior art, the present invention has the following advantages:

The concentration of the shear thickening fluid of the present invention is 0.63-0.65, which is larger than the existing discontinuous shear thickening of all fluids (the ratio of the highest concentration to the lowest concentration exceeds 1000 times at most) and absorbs shock. The energy effect is better, and the anti-impact performance of applied products is also significantly improved.

In the present invention, after premixing nanoparticles, all agglomerated nanoparticle microclusters are broken up by strong shear stress, and then the uniformity of the fluid is improved through a mixing device, and finally the quality of water and small molecule alcohol impurities in the fluid is further controlled through drying. fraction to improve the fluid's ability to absorb energy. The preparation method of the present invention is simple, but it can obtain a stable shear thickening fluid with a fluid concentration of 0.63-0.65, and ensures that the viscosity increases and the fluid absorbs energy better, which opens up the application of shear thickening fluid. Wider scope.

Description of drawings

Figure 1 shows the silica spheres with a particle size of 520±49nm dispersed in relative molecules in Example 1. The relationship between viscosity and shear rate of shear thickening fluids of different concentrations obtained from polyethylene glycol with a mass of 200;

Figure 2A is a graph showing the relationship between the viscosity of the fluid prepared in Example 2-1 and Example 2-2 as a function of shear rate, in which the open circle curve represents fluid 2-1 and the solid square curve represents fluid 2-2;

Figure 2B is a graph showing the relationship between viscosity and shear stress of the fluid prepared in Example 2-1 and Example 2-2, in which the hollow circle curve represents fluid 2-1 and the solid square curve represents fluid 2-2;

Figure 3 is a log-log curve showing the relationship between viscosity and shear stress of the fluid prepared in Example 4;

Figure 4 is a graph showing the change in viscosity of the fluid prepared in Example 5 as a function of shear rate;

Figure 5 is a graph showing the relationship between the viscosity of the fluid prepared in Example 6 and the change in shear rate;

Figure 6 is a graph showing the change in viscosity of the fluid prepared in Example 7 as a function of shear rate.

Detailed ways

An ultra-high concentration shear thickening fluid composed of nanoparticles and solvents with a fluid concentration of 0.63-0.65. The preparation method of the fluid includes the following steps:

a. Prepare the premixed liquid: slowly add the nanoparticles into the solvent, and stir slowly simultaneously to prevent the formation of lumps visible to the naked eye to prepare the premixed liquid;

b. Shear dispersion: Use strong shear dispersion method to process the premixed liquid to obtain the initial fluid. Under the irradiation of the laser pen, the initial fluid should show a good Tyndall effect;

c. Mixing: Use high circulation instruments to further mix the initial fluid to obtain a fluid with good uniformity and no local stratification during flow;

d. Drying: Dry the fluid until the total content of water and small molecular alcohol impurities in the fluid does not exceed 2.5wt%, that is, discontinuous shear thickening fluid is produced;

e. Mix again: Use a high circulation instrument to mix the dried fluid again for a period of time to ensure that the fluid has good uniformity.

Among them, the nanoparticles can be nanosilica spheres or nanocalcium carbonate particles, and the solvent is liquid polyol, such as ethylene glycol, polyethylene glycol 100, polyethylene glycol 200, polyethylene glycol 300, polyethylene glycol 400. The particle size of the nanoparticles is 250-900nm, which is monodisperse, and the difference between the maximum and minimum particle size does not exceed 40%.

The present invention will be further described in detail below with reference to specific examples. The following percentages that are not otherwise specified are all percentages:

Example 1:

Material:

Nanoparticles: Nanosilica spheres with a particle size of 520±49nm,

Solvent: Polyethylene glycol with a relative molecular mass of 200,

Objective: Prepare shear thickening fluids with fluid concentrations of 0.62, 0.63 and 0.64, hereafter referred to as fluid 1-1, fluid 1-2, and fluid 1-3;

The preparation method is:

a. Premixing: Slowly add the silica balls into the polyethylene glycol in batches, and stir slowly until the silica balls added in each batch do not form lumps visible to the naked eye to obtain a premixed liquid;

b. Shear dispersion: Use a high-energy planetary ball mill to disperse for 16-18 hours at a rotation speed of 800 RPM and a mass ratio of grinding beads to premixed liquid of 2:1 to obtain the initial fluid;

c. Mixing: Use a vortex oscillator to mix the initial fluid for no less than 48 hours, so that the fluid will not cause "stratification and disconnection" due to uneven local viscosity when flowing, and a fluid with excellent uniformity will be produced;

d. Drying: Use a vacuum drying oven to dry the fluid at a vacuum of -0.1MPa and a temperature of 85°C until the total content of water and small molecule alcohol impurities in the fluid does not exceed 2.5wt% to produce discontinuous shear thickening fluid;

e. Mix again: You can use the vortex oscillator to mix the dried fluid for 3-5 hours again to ensure the uniformity of the fluid.

A rheometer (MCR302, Anton Paar) was used to characterize the fluids of φ=0.62 fluid (fluid 1-1), φ=0.63 fluid (fluid 1-2) and φ=0.64 fluid (fluid 1-3) prepared in Example 1. Viscosity as a function of shear rate. The test uses a cone-plate test system with a cone angle of 2° and a diameter of 25mm. Before the test, "pre-shearing" treatment is performed to slowly increase the stress from 0.3Pa to 300Pa within 5 minutes, and then slowly reduce the stress to 0.3Pa within the same time to eliminate the unevenness caused by loading the sample. sex. In order to better characterize the changing trend of fluid viscosity under high shear stress, the "control stress" of the rheometer was used to scan the range of shear stress of 10 ^-2 -10 ⁴ Pa, and the results were expressed as It is presented in the form of “viscosity vs shear rate”, as shown in Figure 1.

When φ = 0.62, the concentration of fluid 1-1 reaches the highest value reported. When the shear rate is about 12s ^-1 , the concentration of the fluid jumps from 4 Pa.s to the highest value of 150 Pa.s, with an increase of about 37.5 times (150/4=37.5). When φ=0.63, the concentration of fluid 1-2 increases even more significantly, from the lowest 4 Pa.s to about 1000 Pa.s, an increase of about 250 times. When φ=0.64, fluid 1-3 increases from the lowest 8Pa.s to 10000Pa.s, an increase of about 1250 times. Therefore, every time the volume fraction increases by 1%, the increase in fluid concentration increases significantly, indicating that the fluid with φ≥0.63 absorbs impact energy better than all existing fluids, and the impact resistance of the product is improved more significantly.

Example 2-1:

According to the preparation method of Example 1, silica spheres with a particle size of 520±49 nm and polyethylene glycol with a relative molecular mass of 200 were prepared into fluid 2-1 with φ≈0.63.

Example 2-2:

According to the preparation method of Example 1, minus step c, silica spheres with a particle size of 520±49 nm and polyethylene glycol with a relative molecular mass of 200 are prepared into fluid 2-2 with φ≈0.63.

According to the testing method of Example 1, test and analyze the relationship between the viscosity of fluid 2-1 and fluid 2-2 with shear rate, and the relationship between fluid viscosity and shear stress, and obtain a characteristic rheological performance diagram, as shown in Figure 2A and shown in Figure 2B. As shown in the hollow circle curve in Figure 2A, the fluid 2-1 prepared according to the preparation method of the present invention begins to thicken at a shear rate of 15 s ^-1 , and then the viscosity rises linearly and the shear rate is limited to about 15 s ^-1 . The concentration increase is about 500 times; in Figure 2B, as the shear stress increases, the viscosity of the fluid 2-1 rises linearly. In the relationship between viscosity and shear stress, the slope of the viscosity increase is approximately equal to 1, which is a typical discontinuity. Shear thickening characteristics. For fluid 2-2 with the same concentration but lacking the preparation in step c (solid square curves in Figures 2A and 2B), the concentration increase is only 10 times, and the slope of the concentration increase in Figure 2B is less than 1, and there is no discontinuous shear. Thickening properties.

Example 3:

According to the preparation method of Example 1, step b is omitted, and silica spheres with a particle size of 400±34 nm and polyethylene glycol with a relative molecular mass of 200 are prepared into φ≈0.63 fluid 3-1.

After being left for 24 hours, the silica balls in fluid 3-1 precipitated, causing the fluid to fail to reach a stable state where the rheological properties could be tested.

Example 4:

Using silica spheres with a particle size of 350±62nm and polyethylene glycol with a relative molecular mass of 200 as raw materials, according to the preparation method of Example 1 and controlling the indicators of step d, prepare φ≈0.63, water and small molecules Fluid 4-1 with the total content of alcohol impurities not exceeding 4wt%, φ≈0.63, fluid 4- with the total content of water and small molecule alcohol impurities not exceeding 2.5wt% 2. Fluid 4-3 with φ≈0.63 and the total content of water and small alcohol impurities does not exceed 1.5wt%. According to the testing method of Example 1, a log-log diagram of the relationship between the viscosity of fluid 4-1, fluid 4-2, and fluid 4-3 with shear stress was obtained, as shown in Figure 3.

When the shear stress generated by an external impact on the shear-thickened fluid exceeds a critical value, the nanoparticles in the fluid will instantly aggregate to form particle clusters, absorbing or dissipating the impact energy. The greater the shear stress, the more particle clusters are formed in the fluid, the better the energy absorption effect, and the greater the viscosity of the fluid. A large number of theoretical modeling shows that under ideal circumstances, the viscosity changes with shear stress in an exponential relationship. In the log-log plot of viscosity and shear stress, the increase in viscosity with shear stress should be a straight line, and the closer the slope is to 1, the better the fluid The more it has the characteristics of discontinuous shear thickening, the higher the efficiency of energy absorption per unit volume of fluid.

As shown in Figure 3 for fluid 4-1, fluid 4-2, and fluid 4-3 of Example 4, when the mass fraction of impurities such as water and small molecular alcohols in the fluid is within 1.5-2.5wt%, the viscosity increases. The slope of is very close to 1, indicating that the fluid has the characteristics of discontinuous shear thickening, and the unit volume of fluid absorbs energy well. When the mass fraction of impurities reaches 4wt%, the increase in viscosity with shear stress is very small, indicating that the fluid has lost the discontinuous shear thickening characteristics, and the fluid per unit volume only has weak energy absorption properties. When the mass fraction of impurities continues to increase, the fluid will completely lose its ability to absorb energy. Therefore, the total mass of impurities such as water and small molecular alcohols in the fluid plays a decisive role in whether the fluid has the characteristics of discontinuous shear thickening and whether the fluid per unit volume can absorb energy well.

In addition, because water and small molecule alcohols are more polar than polypolyols, once the content of water and small molecule alcohols exceeds the critical value of 4wt%, the stability of the nanosilica spheres in the polypolyols will be destroyed, resulting in The silica balls precipitate out, causing the fluid to lose discontinuous shear thickening. characteristic.

Example 5:

Take a trace amount of purchased silica nanoparticles, oscillate and disperse them in deionized water, and use a nanoparticle size analyzer (model: Malvern ZetaSizer Nano-S) to perform a DLS (Dynamic Light Scattering) test to determine the particle size of the silica particles. diameter is 273 nm, and has a 10% particle size difference. The particle size measured through electron microscope pictures is 268±22nm, which is basically consistent with the DLS test results. From this, it was confirmed that the particle size of silica was 273 nm, and there was a 10% difference in particle size.

According to the preparation method of Example 1, the nano-silica particles were dispersed in polyethylene glycol with a relative molecular mass of 100 to obtain a shear thickening fluid with a volume fraction of 0.65. The Control Stress mode of the rheometer (Anton Paar MCR302) was used to scan the shear stress 10 ^-2 -10 ³ to characterize the rheological properties of the fluid, and the results are shown in Figure 4. It can be seen from the change curve of viscosity with shear rate that the viscosity increases suddenly when the shear rate is about 1s ^-1 , which has the characteristics of discontinuous shear thickening. When the viscosity of the fluid rises to 2000 Pa.s, as the shear rate increases, the viscosity of the fluid enters a plateau value and remains at around 3000 Pa.s. This is not because the viscosity of the fluid has risen to the extreme value, but because the viscosity of the fluid is too high, which causes excessive thickening of the fluid and causes slippage with the cone and plate testing system. Therefore, the rheometer cannot measure the highest viscosity value of the fluid.

Example 6:

The particle size of the purchased nanosilica was measured and confirmed to be 556 nm according to the method of Example 5, with a particle size difference of approximately 8%.

According to the method of Example 1, the nano-silica particles were dispersed in polyethylene glycol with a relative molecular mass of 200 to obtain a shear thickening fluid with a particle volume fraction of 0.632. The rheology of the fluid was tested according to the method of Example 5, as shown in Figure 5. From Figure 5 we can It can be seen that the fluid has discontinuous shear thickening characteristics.

Example 7:

The particle size of the purchased calcium carbonate particles was measured and confirmed to be 853 nm according to the method of Example 5, and had a particle size difference of approximately 25%.

According to the method of Example 1, the calcium carbonate particles were dispersed in polyethylene glycol with a relative molecular mass of 200 to obtain a shear thickening fluid with a volume fraction of 0.63. The rheology of the fluid was tested according to the method of Example 5, as shown in Figure 6. As can be seen from Figure 6, the fluid has the characteristics of discontinuous shear thickening.

Claims

An ultra-high concentration shear thickening fluid is composed of nanoparticles and a solvent, characterized in that the volume fraction of the nanoparticles in the fluid is 0.63-0.65, and the solvent is liquid polyol.
The ultra-high concentration shear thickening fluid according to claim 1, characterized in that the particle size of the nanoparticles is 250-900 nm, and the particle size is monodisperse.
The ultra-high concentration shear thickening fluid according to claim 1, characterized in that the nanoparticles are selected from inorganic compounds and are silica or calcium carbonate.
A method for preparing ultra-high concentration shear thickening fluid according to claim 1, characterized by comprising the following steps:

a. Premixing: Slowly add the nanoparticles into the solvent and stir slowly until there are no lumps visible to the naked eye to obtain a premixed solution;

b. Shear dispersion: The particles in the premixed liquid are strongly sheared and dispersed to form an initial fluid. The "Tyndale effect" of the initial fluid is visible to the naked eye under the irradiation of the laser pen;

c. Mixing: Use high circulation instruments to further mix the initial fluid to obtain a fluid with good uniformity;

d. Drying: Dry the fluid until the total content of water and small molecular alcohol impurities in the fluid does not exceed 3.5wt%, that is, discontinuous shear thickening fluid is produced.
A method for preparing ultra-high concentration shear thickening fluid according to claim 4, characterized in that the dried fluid can be mixed again by repeating step c to improve the uniformity of the entire fluid.
A method for preparing ultra-high concentration shear thickening fluid according to claim 4, characterized in that the instrument for strong shearing in step b is a ball mill or a bead mill or a three-roller.
A method for preparing ultra-high concentration shear thickening fluid according to claim 4, characterized in that the high circulation instrument is a vortex oscillator or a bottle roller.
An application of ultra-high concentration shear thickening fluid according to claim 1.
An application of ultra-high concentration shear thickening fluid according to claim 8, characterized in that it is applied to composite anti-thorn materials or anti-collision protection bodies.